Liquid crystal projector

ABSTRACT

The present invention provides a liquid crystal projector including a plurality of liquid crystal panels, a prism for compositing the modulated plural color lights to generate a color image, top and bottom metal plates disposed above and below the prism, and an optical system for magnifying and projecting the generated color image, wherein the liquid crystal panels are directly adhered to metal hold plates, and the metal hold plates are fixed to the top and bottom metal plates such that the emergent surfaces of the liquid crystal panels face the incident surfaces of the prism. Further, a closed space is provided between the incident surfaces of the prism and the emergent surfaces of the liquid crystal panels so as to prevent air contaminants from effecting the performance of the device.

This application claims priority to International Application No.PCT/JP02/08222, filed Aug. 12, 2002, and Japanese Patent Application No.JP2001-255628, filed Aug. 27, 2001, each of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a liquid crystal projector, inparticular, to a liquid crystal projector which has liquid crystalpanels fixed to a dichroic prism under improved fixation configuration.

BACKGROUND ART

Generally, a liquid crystal projector includes a plurality of liquidcrystal panels for modulating red (R), green (G), and blue (B) lightsrespectively, a dichroic prism for compositing thus modulated R, G, andB lights to generate a color image, and an optical system such as aprojection lens for magnifying and projecting thus generated colorimage.

In a liquid crystal projector of this kind, respective color lightsmodulated by a plurality of liquid crystal panels are composited by adichroic prism. So as to align pixels of respective liquid crystalpanels to superpose projected images generated by respective liquidcrystal panels onto a screen with high accuracy, such a liquid crystalprojector is required to have an adjustment mechanism along the upwardand downward, leftward and rightward, and rotation direction. Also, anadjustment mechanism for focusing along the forward and backward,pitching, and yawing direction is necessary so as to accurately bringfocal points of projected images onto a screen into focus. In case of anoptical prism unit having such adjustment mechanisms united therein, itbecomes difficult to reduce the adjustment mechanisms in size when thesize of liquid crystal panels is smaller than is predetermined. The moreadjustment mechanisms become accurate for fine adjustment, the largerthe adjustment mechanisms become in size. Thus, even though liquidcrystal panels themselves are reduced in size, it is difficult to reducean optical prism unit itself and a liquid crystal projector itself insize in view of their configuration under the constraint in size oftheir adjustment mechanisms. There is proposed a liquid crystalprojector which has liquid crystal panels directly adhered to be fixedto a dichroic prism, excluding above-described adjustment mechanisms forthe purpose of miniaturization. However, in case defect is detected in aliquid crystal panel, it is difficult to exchange only the defectiveliquid crystal panel after adhering the liquid crystal panel to adichroic prism. So, even though defect is detected in only one liquidcrystal panel, a unit of dichroic prism including the defective liquidcrystal panel as well as other non-defective liquid crystal panels hasto be exchanged, which is not economic.

There is also proposed a liquid crystal projector which has a panelfixation frame fixed to a dichroic prism, and has liquid crystal panelsfixed to the panel fixation frame, excluding adjustment mechanisms froman optical unit. In this case, the liquid crystal projector is providedwith a space or an air gap between the emergent surfaces of the liquidcrystal panels and the incident surfaces of a dichroic prism. In the airgap, polarizing plates of the emergent sides are also provided. Thus,there is raised a problem that dust, which is scattered by a cooling fanfor cooling liquid crystal panels, may break into the air gap and stickto the polarizing plates and the liquid crystal panels. Dust which islarger than is predetermined against the pixel size has a bad influenceon the quality of projected images. The smaller the liquid crystalpanels become, the more the problem of dust becomes serious.

As a liquid crystal panel is miniaturized, the density of an incidentlight from a light source increases, which subsequently increases theoperation temperature of the liquid crystal panel. Furthermore, as aliquid crystal projector is miniaturized, an optical prism unit is alsorequired to be miniaturized. In this case, it is predicted that theoperation temperature undesirably exceed the top temperature limit underwhich emergent-side polarizing plates and liquid crystal panels cannotoperate, which problem should be definitely solved. In a liquid crystalprojector, polarizing plates located at the emergent sides and liquidcrystal panels absorb lights from light sources and generate heat. Suchpolarizing plates and liquid crystal panels are made of organicmaterial, and it is required that the operation temperature thereof besuppressed under 70° C. in enhancing the credibility of the operation ofa liquid crystal projector.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention has an object to overcome theabove-mentioned drawbacks of the prior art by providing a liquid crystalprojector which has liquid crystal panels fixed to a prism underimproved fixation configuration, which enables exchange of parts orelements easily, and has sufficient capability of radiating heat, andcan also prevent sticking of dust.

The above object can be attained by providing a liquid crystal projectorincluding a plurality of liquid crystal panels for modulating aplurality of color lights respectively, a prism for compositing thusmodulated plural color lights to generate a color image, and an opticalsystem for magnifying and projecting thus generated color image, whereinthe liquid crystal panels are directly adhered to metal hold plates, andthe metal hold plates are fixed to the prism such that the emergentsurfaces of the liquid crystal panels face the incident surfaces of theprism. The liquid crystal panels preferably have glass sheets havingthermal conductivity fixed to the incident surfaces thereof. Radiationfins are fixed to the prism with the metal hold plates and the glasssheets having thermal conductivity brought into contact with the fins. Aclosed space is provided between the incident surfaces of the prism andthe emergent surfaces of the liquid crystal panels so as to prevent airflow, and at least polarizing plates are arranged in the closed space.The polarizing plates are arranged at the incident sides of the prism,and thermal conduction members for absorbing heat generated in thepolarizing plates may be arranged in the closed space.

According to the liquid crystal projector of the present invention, theliquid crystal panels are directly adhered to metal hold plates, and themetal hold plates are fixed to the prism such that the emergent surfacesof the liquid crystal panels face the incident surfaces of the prism. Byemploying this configuration, an optical prism unit united with liquidcrystal panels can be reduced in size, and can be exchanged easily whendefect is detected in a liquid crystal panel. The liquid crystal panels,which are directly adhered to metal hold plates excellent in thermalconductivity, are excellent in heat radiation. Furthermore, the liquidcrystal panels have glass sheets made of such as sapphire glass havingthermal conductivity fixed to the incident surfaces thereof. Also,radiation fins are fixed to the prism with the metal hold plates and theglass sheets having thermal conductivity brought into contact with thefins. By employing this configuration, the liquid crystal panels can beefficiently cooled. In addition, a closed space or an air gap isprovided between the incident surfaces of the prism and the emergentsurfaces of the liquid crystal panels so as to prevent air flow, whichcan prevent dust from breaking into the air gap and sticking to thepolarizing plates and the liquid crystal panels arranged therein.

These objects and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription of the preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded view of an optical prism unit configuring theprincipal portion of the liquid crystal projector employing the presentinvention.

FIG. 2 shows an enlarged sectional view of the optical prism unit shownin FIG. 1.

FIG. 3 shows a block diagram indicating radiation paths for radiatingheat in the configuration of the liquid crystal projector employing thepresent invention.

FIG. 4 shows a schematic perspective view of the assembled state of theoptical prism unit of the liquid crystal projector employing the presentinvention.

FIG. 5 shows a schematic plan view of the optical prism unit of theliquid crystal projector employing the present invention.

FIG. 6 shows a schematic plan view of another example of an opticalprism unit of the liquid crystal projector employing the presentinvention.

FIG. 7 shows an exploded view of another example of an optical prismunit configuring the principal portion of the liquid crystal projectoremploying the present invention.

FIG. 8 shows an enlarged sectional view of the optical prism unit of theliquid crystal projector shown in FIG. 7.

FIG. 9 shows a block diagram indicating radiation paths for radiatingheat in the configuration of the liquid crystal projector shown in FIG.7.

BEST MODE FOR CARRYING OUT THE INVENTION

The liquid crystal projector employing the present invention willfurther be described below concerning the best modes with reference tothe accompanying drawings.

FIG. 1 shows an exploded view of an optical prism unit configuring theprincipal portion of the liquid crystal projector employing the presentinvention.

In the liquid crystal projector shown in FIG. 1, only one liquid crystalpanel 1 is shown in the optical prism unit, which actually has aplurality of liquid crystal panels, so as to simplify the drawing forthe convenience of simple comprehension. The liquid crystal panel 1 hastwo glass basal sheets joined together with liquid crystal enclosedtherebetween, and a flat cable for external connection fixed thereto, asshown in FIG. 1.

The liquid crystal projector further has a dichroic prism 2 formed inthe shape of a cube, which is sandwiched between an upper plate 4 and alower plate 5. The upper plate 4 and the lower plate 5, which are madeof metal material such as aluminum, conduct heat. The liquid crystalpanel 1 is adhered to be fixed to a hold plate 3 which is also made ofaluminum, etc. The hold plate 3 having the liquid crystal panel 1adhered to be fixed thereto is fixed to the upper plate 4 and to thelower plate 5 using screws 6. Also, a pair of radiation fins 8 forcooling are fixed to the upper plate 4 and to the lower plate 5 usingscrews 6 with the hold plate 3 sandwiched therebetween.

A glass sheet 7 made of such as sapphire glass having high thermalconductivity is fixed to the incident surface of the liquid crystalpanel 1. A polarizing plate 9 and a phase difference plate 10 arearranged in a space provided between the incident surface of thedichroic prism 2 and the emergent surface of the liquid crystal panel 1.The polarizing plate 9 and the phase difference plate 10 are adhered tobe fixed to the emergent surface of the liquid crystal panel 1 usingadhesive. The glass sheet 7 fixed to the incident surface of the liquidcrystal panel 1 is brought into contact with the radiation fins 8directly or indirectly via jointing material such as silicon greasehaving high thermal conductivity.

Thus, the liquid crystal projector employing the present invention hasthe liquid crystal panel 1 directly adhered to be fixed to the metalhold plate 3, which can radiate heat generated at the liquid crystalpanel 1.

In a liquid crystal projector, which has its liquid crystal panel 1enclosed in a protection frame made of plastic, the liquid crystal panel1 is arranged via such protection frame. On the other hand, in theliquid crystal projector of the present. invention, the liquid crystalpanel 1 itself is directly fixed to the metal hold plate 3 so as toimprove cooling efficiency. Also, the liquid crystal panel 1 can beeasily exchanged by loosening screws 6 and removing the hold plate 3from the upper plate 4 and the lower plate 5, so the liquid crystalpanel 1 can be exchanged easily. The glass sheet 7 is fixed to theincident surface of the liquid crystal panel 1. Thus, the outer surfaceof the liquid crystal panel 1 is protected, and cooling efficiency isimproved. The metal hold plate 3 and the glass sheet 7 are physicallybrought into contact with the radiation fins 8, which improves coolingefficiently owing to thermal conduction.

FIG. 2 shows an enlarged sectional view of the optical prism unit shownin FIG. 1, which schematically shows fixing configuration of the liquidcrystal panel 1.

The liquid crystal panel 1 is fixed to the metal hold plate 3 usingadhesive 11, as shown in FIG. 2. The hold plate 3 is fixed to the upperplate 4 and to the lower plate 5 arranged at the side of the dichroicprism 2 using screws 6. At this time, the radiation fins 8 are fixed tothe upper plate 4 and to the lower plate 5 with the hold plate 3sandwiched therebetween. The glass sheet 7 made of such as sapphireglass is fixed to the incident surface of the liquid crystal panel 1.The glass sheet 7 having high thermal conductivity is brought intocontact with the radiation fins 8 directly or indirectly via silicongrease etc., and heat generated at the liquid crystal panel 1 isconducted to the radiation fins 8. The polarizing plate 9 and the phasedifference plate 10 are arranged in an air gap partitioned by theincident surface of the dichroic prism 2 and the emergent surface of theliquid crystal panel 1. In the embodiment, the polarizing plate 9 andthe phase difference plate 10 are fixed to the emergent surface of theliquid crystal panel 1, while the present invention is not restricted tothe embodiment, and the polarizing plate 9 and the phase differenceplate 10 may be fixed to the incident surface of the dichroic prism 2.

FIG. 3 shows a block diagram indicating radiation paths for radiatingheat in the configuration shown in FIG. 1 and FIG. 2.

Heat generated from the liquid crystal panel and the emergent-sidepolarizing plate being heat sources is radiated into the atmospherethrough mainly three radiation paths, as shown in FIG. 3. That is, partof heat generated from the liquid crystal panel and the emergent-sidepolarizing plate is directly radiated into the atmosphere via the glasssheet made of sapphire glass etc. having high thermal conductivity. Partof heat conducted to the glass sheet is further conducted to theradiation fins, and thus conducted heat is radiated into the atmosphere.Other part of heat generated from the heat sources is conducted to themetal hold plate, and thus conducted heat is radiated into theatmosphere from the radiation fins. By thus radiating heat through thethree radiation paths, the liquid crystal panel and the emergent-sidepolarizing plate can be efficiently cooled. By developing such a heatconduction and radiation configuration, heat generated from heat sourcescomposed of the liquid crystal panel and the emergent-side polarizingplate is actively radiated into the atmosphere.

In the conventional liquid crystal projector, heat generated from aliquid crystal panel and an emergent-side polarizing plate is cooled attheir surfaces by only air flows generated from a cooling fan.

On the other hand, according to the present invention, heat generatedfrom the heat sources is conducted to outside rapidly through mainlythree radiation paths, as shown in FIG. 3, which can efficiently coolthe liquid crystal panel and the emergent-side polarizing plate. Thatis, cooling capability can be improved. Thus, in case an optical lightof the same light quantity falls on the liquid crystal panel, eventhough rotational frequency of a cooling fan is decreased, temperatureof the liquid crystal panel and the emergent-side polarizing plate canbe suppressed by about the same extent as that of conventionalconfiguration. When rotational frequency of a cooling fan is decreased,noise of the cooing fan can be suppressed.

Conventionally, the transparent glass sheet which is fixed to theincident surface of the liquid crystal panel is made of neoceram, andhas its transmission surface coated with a reflection reducing film.Even though foreign matter such as dust sticks to the incident surfaceof the glass sheet, being defocused at the imaging focal point,actually, sticking of foreign matter such as dust can be ignored. In thepresent invention, by replacing the glass sheet, adopted for dustproofing, made of neoceram with that made of such as sapphire glasshaving high thermal conductivity, cooling function as well as dustproofing function can be obtained, which can reduce the cost.

FIG. 4 shows a schematic perspective view of the assembled state of theoptical prism unit of the liquid crystal projector shown in FIG. 1.

The dichroic prism 2 formed approximately in the shape of a cube has theupper plate 4 made of such as aluminum fixed to the top thereof, andalso has the lower plate 5 or base plate also made of such as aluminumfixed to the bottom thereof, as shown in FIG. 4. For a pair of the upperand lower plates 4 and 5, liquid crystal panels 1R, 1G, and 1B for R, G,and B lights are fixed. The liquid crystal panel 1R is fixed to theupper and lower plates 4 and 5 with the hold plate 3 adhered to be fixedthereto together with a pair of the upper and lower radiation fins 8using screws. Similarly, the liquid crystal panel 1G is fixed to theadjacent incident surface of the dichroic prism 2 via the hold plate.Also, the liquid crystal panel 1B is fixed to the incident surface,opposite to the liquid crystal panel 1R, of the dichroic prism 2 via thehold plate. Thus, liquid crystal panels 1R, 1G, and 1B for R, G, and Blights are fixed to the three incident surfaces of the dichroic prism 2,and the residual one surface remains opened from which a projectionimage is emerging. A cooling fan, not shown, is arranged so that coolingair flows Ec pass through the radiation fins 8.

FIG. 5 shows a schematic plan view of the optical prism unit shown inFIG. 4.

The liquid crystal panels 1R, 1G, and 1B are fixed to the three sides ofa square indicating the dichroic prism 2 via the hold plates 3, as shownin FIG. 5. A projection lens 20 being an optical system having aprojection lens is so arranged as to face the residual one side of thesquare. There is provided a space between the dichroic prism 2 and thehold plate 3 having the liquid crystal panel 1R adhered to be fixedthereto, and the space is closed by a packing 30. Also, there isprovided a space between the dichroic prism 2 and the hold plate 3having the liquid crystal panel 1B adhered to be fixed thereto, and thespace is closed by a packing 30. As has been described hereinbefore, theliquid crystal projector includes the multiple liquid crystal panels 1R,1G, and 1B for modulating R, G, and B lights, the dichroic prism 2 forcompositing thus modulated R, G, and B lights to generate a color image,and an optical system of the projection lens 20 for magnifying andprojecting thus generated color image. The liquid crystal panels 1R, 1G,and 1B are directly adhered to be fixed to the metal hold plates 3, andthe hold plates 3 are fixed to the dichroic prism 2 such that theemergent surfaces of the respective liquid crystal panels face thecorresponding incident surfaces of the dichroic prism 2. The space (airgap) provided between the incident surfaces of the dichroic prism 2 andthe emergent surfaces of the respective liquid crystal panels 1R, 1G,and 1B is closed by packings 30 so as to prevent air flow. Also, atleast polarizing plates, not shown, are provided in the air gap.

As has been described above, the three incident surfaces of the dichroicprism 2 are enclosed by the liquid crystal panels 1R, 1G, and 1B, thehold plates 3, and adhesive. Also, the top and the bottom of thedichroic prism 2 are directly enclosed by the upper plate 4 and thelower plate 5. Around the emergent surface of the dichroic prism 2 whichfaces the projection lens 20, there are provided spaces at an endsurface of the hold plate 3 having the liquid crystal panel 1R adheredto be fixed thereto and at an end surface of the hold plate 3 having theliquid crystal panel 1B adhered to be fixed thereto, and the spaces areclosed by the packings 30. Thus, the respective incident surfaces of thedichroic prism 2 facing the respective liquid crystal panels 1R, 1G, and1B are shielded from outside so as to prevent cooling air flows fromentering. Thus, dust carried by cooling air flows Ec is prevented fromsticking to the liquid crystal panels and the polarizing plates.

FIG. 6 shows another example of the optical prism unit shown in FIG. 5.In the example shown in FIG. 6, instead of the packings 30 for enclosinga space, a dummy glass sheet 40 is arranged at the side of the emergentsurface of the dichroic prism 2. The dummy glass sheet 40 is joined tothe adjacent hold plates 3, and four surfaces of the dichroic prism 2are completely sealed. Also, the top and the bottom of the dichroicprism 2 are completely sealed by the upper plate 4 and the lower plate5. Thus, the air gap provided between the dichroic prism 2 and therespective liquid crystal panels 1R, 1G, and 1B can be completelysealed.

FIG. 7 shows an exploded view of another example of an optical prismunit configuring the principal portion of the liquid crystal projectoremploying the present invention, and parts or components similar tothose of the liquid crystal projector shown in FIG. 1 are indicated withthe same reference numerals. The point different from that of the liquidcrystal projector shown in FIG. 1 is that the phase difference plate 10and the polarizing plate 9 are fixed not to the liquid crystal panel 1but to a transparent glass sheet 15 made of such as sapphire glasshaving high thermal conductivity, and the glass sheet 15 is adhered tobe fixed to the incident surface of the dichroic prism 2. Furthermore, aplate spring 17 and a spring bracket 16 are used so as to efficientlyconduct heat generated from the glass sheet 15.

FIG. 8 shows an enlarged sectional view of the optical prism unit of theliquid crystal projector shown in FIG. 7, which schematically showsfixing configuration of the liquid crystal panel 1. Parts or componentssimilar to those of the liquid crystal projector shown in FIG. 2 areindicated with the same reference numerals.

The polarizing plate 9 and the phase difference plate 10 are fixed tothe glass sheet 15, as shown in FIG. 8. The glass sheet 15 is adhered tobe fixed to the incident surface of the dichroic prism 2. The platespring 17 abuts on the glass sheet 15. Spring portions of the platespring 17 are sandwiched between the incident surface of the dichroicprism 2 and the metal hold plate 3. The spring bracket 16 is arranged soas to support the plate spring 17. Thus, heat absorbed by the polarizingplate 9 is efficiently radiated to outside via the plate spring 17 andthe spring bracket 16.

FIG. 9 shows a block diagram indicating radiation paths for radiatingheat in the configuration shown in FIG. 7 and FIG. 8. Radiation blockssimilar to those shown in FIG. 3 are indicated with the same blocks.

As has been described above, the liquid crystal panel and theemergent-side polarizing plate are the main heat sources of the liquidcrystal projector. Heat generated from the liquid crystal panel isdirectly radiated into the atmosphere via the glass sheet which is fixedto the incident surface thereof. Otherwise, heat conducted to the glasssheet is further conducted to radiation fins, and thus conducted heat isradiated into the atmosphere from the radiation fins. Furthermore, heatgenerated from the liquid crystal panel is conducted to the metal holdplate, and thus conducted heat is radiated into the atmosphere from theradiation fins. These radiation paths for radiating heat are similar tothose shown in FIG. 3. In the present embodiment, the emergent-sidepolarizing plate is separated from the liquid crystal panel to formother radiation paths. Firstly, heat generated from the emergent-sidepolarizing plate is conducted to the dichroic prism via the glass sheethaving thermal conductivity, and thus conducted heat is radiated intothe atmosphere from the upper plate via the radiation fins or from thelower plate via the radiation fins. Furthermore, heat generated from theemergent-side polarizing plate is conducted to the spring bracket andthen to the plate spring, and is further conducted to the metal holdplate, and thus conducted heat is radiated into the atmosphere from theradiation fins. In this configuration, heat generated from the liquidcrystal panel and the emergent-side polarizing plate is radiated intothe atmosphere through mainly two radiation paths, which can furtherimprove cooling capability. Thus, even though the liquid crystal panelis miniaturized and heating value is increased, the liquid crystalprojector of this configuration can cope with the situation. Sincerotational frequency of a cooling fan can be decreased, the problem ofnoise of the cooing fan can be solved when household liquid crystalprojectors are diffused.

In this configuration, the emergent surface of the liquid crystal paneland the emergent-side polarizing plate are enclosed by the hold plate.Thus, cooling air from the cooling fan does not flow directly to theliquid crystal panel and to the emergent-side polarizing plate, whichcan prevent dust from sticking to the liquid crystal panel and to theemergent-side polarizing plate. Furthermore, it is possible to replacesingle liquid crystal panel after assembling the optical prism unit.

In the above-described embodiments, the radiation fins for each liquidcrystal panel, which are separated or composed of an upper fin and alower fin, may be united into one. On the other hand, the radiation finsmay be of different configuration. For example, slits of the radiationfins, which are formed along the longitudinal direction in theembodiments, may be formed along the oblique direction so as to usecooling air efficiently. Moreover, protrusion lengths of the upper finand the lower fin may be different. Furthermore, a parting plate may bearranged at the incident side or at the emergent side so as to improveoptical properties.

INDUSTRIAL APPLICABILITY

As in the above, according to the present invention, since rotationalfrequency of a cooling fan can be decreased, a liquid crystal projectorwith suppressed fan noise can be provided. Since temperature of liquidcrystal panels and emergent-side polarizing plates can be kept low,credibility and commercial value of a liquid crystal projector can beimproved. An optical prism unit is not required to have adjustmentmechanisms united therein, which can miniaturize a liquid crystalprojector. Even though liquid crystal panels are miniaturized andheating value is increased, a liquid crystal projector can cope with thesituation. Since rotational frequency of a cooling fan can be decreased,the problem of noise of the cooing fan can be solved when householdliquid crystal projectors are diffused. Protection frames or enclosuresmade of resin fixed to conventional liquid crystal panels can beexcluded, which can reduce the cost. Glass sheets have cooling functionas well as dust proofing function, which can reduce the cost. Also,since an air gap is provided between a prism and liquid crystal panels,and the liquid crystal panels are not adhered to the prism, air bubblesare prevented from occurring between the liquid crystal panels and theprism, which can improve image quality.

What is claimed is:
 1. A liquid crystal projector, comprising: a plurality of liquid crystal panels each of which provides a color output; a prism for compositing the color output lights to generate a color image; and metal plates disposed on sides of the prism; and an optical system for magnifying and projecting the generated color image; wherein the liquid crystal panels are each respectively directly adhered to a corresponding metal hold plates, and the metal hold plates are fixed to the metal plates such that the emergent surfaces of the liquid crystal panels face the incident surfaces of the prism.
 2. The liquid crystal projector as set forth in claim 1, wherein the liquid crystal panels have thermally conductive glass sheets fixed over incident surfaces thereof.
 3. The liquid crystal projector as set forth in claim 2, wherein radiation fins are fixed to the prism via the metal hold plates.
 4. The liquid crystal projector as set forth in claim 1, wherein a sealed closed space is provided between the incident surfaces of the prism and the emergent surfaces of the liquid crystal panels, and at least one polarizing plate is arranged in the closed space.
 5. The liquid crystal projector as set forth in claim 4, wherein polarizing plates are arranged at incident sides of the prism, and thermal conduction members for absorbing heat generated in the polarizing plates are arranged in the closed space provided between the incident surfaces of the prism and the emergent surfaces of the liquid crystal panels. 